Swift 3.0非常简单的实现将是:

func dateByAddingDays(inDays: Int) -> Date {
    let today = Date()
    return Calendar.current.date(byAdding: .day, value: inDays, to: today)!
}

Swift 5.0:

var dayComponent    = DateComponents()
dayComponent.day    = 1 // For removing one day (yesterday): -1
let theCalendar     = Calendar.current
let nextDate        = theCalendar.date(byAdding: dayComponent, to: Date())
print("nextDate : \(nextDate)")

目标C:

NSDateComponents *dayComponent = [[NSDateComponents alloc] init];
dayComponent.day = 1;

NSCalendar *theCalendar = [NSCalendar currentCalendar];
NSDate *nextDate = [theCalendar dateByAddingComponents:dayComponent toDate:[NSDate date] options:0];

NSLog(@"nextDate: %@ ...", nextDate);

这应该是不言而喻的。

它的工作原理!

NSCalendar *calendar = [NSCalendar currentCalendar];
NSCalendarUnit unit = NSCalendarUnitDay;
NSInteger value = 1;
NSDate *today = [NSDate date];
NSDate *tomorrow = [calendar dateByAddingUnit:unit value:value toDate:today options:NSCalendarMatchStrictly];

简单的Swift扩展昨天和明天从任何日期:

extension Date {
    
    var previousDay: Date {
        Calendar.current.date(byAdding: DateComponents(day:-1), to: self)!
    }
    
    var nextDay: Date {
        Calendar.current.date(byAdding: DateComponents(day:+1), to: self)!
    }
    
}

我在这里根据问题中的建议强制展开可选选项: 何时dateByAddingComponents:toDate:options返回nil?

在swift中，您可以在NSDate中添加扩展方法

extension NSDate {
    func addNoOfDays(noOfDays:Int) -> NSDate! {
        let cal:NSCalendar = NSCalendar.currentCalendar()
        cal.timeZone = NSTimeZone(abbreviation: "UTC")!
        let comps:NSDateComponents = NSDateComponents()
        comps.day = noOfDays
        return cal.dateByAddingComponents(comps, toDate: self, options: nil)
    }
}

你可以用这个

NSDate().addNoOfDays(3)

基于highmaintenance的回答和vikingosegundo的评论，一个工作的Swift 3+实现。这个日期扩展也有额外的选项来改变年，月和时间:

extension Date {

    /// Returns a Date with the specified amount of components added to the one it is called with
    func add(years: Int = 0, months: Int = 0, days: Int = 0, hours: Int = 0, minutes: Int = 0, seconds: Int = 0) -> Date? {
        let components = DateComponents(year: years, month: months, day: days, hour: hours, minute: minutes, second: seconds)
        return Calendar.current.date(byAdding: components, to: self)
    }

    /// Returns a Date with the specified amount of components subtracted from the one it is called with
    func subtract(years: Int = 0, months: Int = 0, days: Int = 0, hours: Int = 0, minutes: Int = 0, seconds: Int = 0) -> Date? {
        return add(years: -years, months: -months, days: -days, hours: -hours, minutes: -minutes, seconds: -seconds)
    }

}

如果按照OP的要求只增加一天，则用法如下:

let today = Date() // date is then today for this example
let tomorrow = today.add(days: 1)